Exception when decoding map

[jakubgwozdz]

Having this code:

@Serializable
private data class TestData(
    val text: String,
    val map: Map<String, String>,
    val number: Int,
)
fun main() {
    val data = TestData(text = "text value", number = 7321, map = mapOf("a" to "b"))
    val encoded = Toml.encodeToString(data)
    println("=====\n$encoded\n=====")
    val decoded: TestData = Toml.decodeFromString(encoded) // throws MissingRequiredPropertyException
}

The output is this:

=====
text = "text value"
number = 7321

[map]
    a = "b"
=====
Exception in thread "main" com.akuleshov7.ktoml.exceptions.MissingRequiredPropertyException: Invalid number of key-value arguments provided in the input for deserialization. Missing required property <0> from class <kotlin.collections.LinkedHashMap> in the input. (In your deserialization class you have declared this field, but it is missing in the input)
    at com.akuleshov7.ktoml.decoders.TomlMainDecoder.checkMissingRequiredProperties(TomlMainDecoder.kt:192)
    at com.akuleshov7.ktoml.decoders.TomlMainDecoder.iterateOverStructure(TomlMainDecoder.kt:243)
    at com.akuleshov7.ktoml.decoders.TomlMainDecoder.beginStructure(TomlMainDecoder.kt:212)

Encoding works perfectly well and toml content is generated without problems, but decoding this content back - well, we're not there yet :)

[orchestr7]

will be investigated this month

[orchestr7]

thank you for your report and sorry for a long delay!

[y9san9]

Still having the issue, is there any workaround? Really need to deserialize libs.versions.toml

[orchestr7]

@y9san9 sorry for a stupid question, what is the datastucture in toml reflects Maps? Cannot find a simple example.

Any string that you are trying to decode?

[y9san9]

Your class Toml produces from:

Toml.encodeToString(mapOf("library" to "1.0.0", "kotlin" to "2.0.0")) 

The following:

library = "1.0.0"
kotlin = "2.0.0"

And I want to decode that back, but cannot do that at the moment. All Toml spec is about to be converted to hash tables (probably that's something similar to hash maps)

[orchestr7]

Hm, but it's a little bit weird actually:

library = "1.0.0"
kotlin = "2.0.0"

is not a Map... It's a number of properties in Toml specification.

To store it to the map, I will need to guess the type somehow and understand that it is really a Map, but not a property, that user forgot to provide (due to his manual bug).

[y9san9]

So how could I deserialize that?

And also that:

coreKtx = { module = "androidx.core:core-ktx", version.ref = "coreKtx" }

All the solutions I found did that using Map

[y9san9]

(I don't know the exact names, I want to deserialize arbitrary amount of such rows)

[orchestr7]

So how could I deserialize that?

And also that:

coreKtx = { module = "androidx.core:core-ktx", version.ref = "coreKtx" }

All the solutions I found did that using Map

hm, let me look into the spec of TOML

[orchestr7]

So how could I deserialize that?

And also that:

coreKtx = { module = "androidx.core:core-ktx", version.ref = "coreKtx" }

All the solutions I found did that using Map

According to the spec, it's Inline Table https://toml.io/en/v1.0.0#inline-table and we should be able to decode it 🤔

[y9san9]

A list of inline tables? If so, that doesn't work either.

@Serializable
data class Libraries(
    val libraries: List<@TomlInlineTable Library>
) {
    @Serializable
    data class Library(val module: String, val version: String)
}

How do I get coreKtx with such setup?

[y9san9]

The intuitive approach: to add pair name -> inline table I used the Map type, which is also being encoded in such structure I needed, but is not being decoded back

[orchestr7]

A list of inline tables?

I think that this might help: https://github.com/akuleshov7/ktoml#how-ktoml-works-examples

We actually had a test and an example for such structures: gradle-libs-like-property = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }

your class:
    @SerialName("gradle-libs-like-property")
    val kotlinJvm: GradlePlugin

@Serializable
data class GradlePlugin(val id: String, val version: Version)

But actually I do not like the behaviour when we create a map on serialization and then have ambiguity on the deserialisation with the same class. I understood the problem, but do Inline Tables will help you now in your particular case?

[y9san9]

Sorry, as I mentioned earlier that I don't know what names of the libraries will be. I want to parse them and only after that I could tell the names.

[y9san9]

In Json when you don't know class layout you would also use Map<String, JsonElement>

[orchestr7]

Sorry, as I mentioned earlier that I don't know what names of the libraries will be. I want to parse them and only after that I could tell the names.

Got it, so you need to parse properties without explicit naming, and you need to decode it to some map of strings. I do not have an idea of how to support it now, as it is violating TOML spec, but I will think...

[y9san9]

Why is it violating TOML specs? It's how Version Catalogs work :)

[orchestr7]

Why is it violating TOML specs? It's how Version Catalogs work :)

Yes, I mean that the idea of TOML is that you know the names of the properties. That's why this structure:

a = 1

is a NAMED key-value property https://toml.io/en/v1.0.0#keyvalue-pair

It will be a different story to decode the following code:

a = 1
b = 2

to a Map("a" to "1", "b" to "2"), because the original idea is about named keys with typed values:

val a: Int
val b: Int

[orchestr7]

BUT! Ktoml itself has multiple extensions to the original idea of TOML, so probably we can think of something we can do here. Especially when we encode these values to a Map. Need to think...

[orchestr7]

Initial implementation is done for simple map: https://github.com/akuleshov7/ktoml/pull/246 (phase 1) @jakubgwozdz @y9san9

Phase 2 with nested tables: WIP

[orchestr7]

Nested Maps (nested tables) done in #252

[orchestr7]

Released in 0.5.1